Neutrino Karma Preset

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neutrino-preset-karma is a Neutrino preset that supports testing web applications using the Karma test runner.


  • Zero upfront configuration necessary to start testing on real browsers with Karma, Mocha, and Chrome
  • Babel compilation that compiles your tests using the same Babel options used by your source code
  • Source watching for re-running of tests on change
  • Out-of-the-box support for running in CI
  • Easily extensible to customize your testing as needed


  • Node.js v6.10+
  • Yarn or npm client
  • Neutrino v6, Neutrino build preset


neutrino-preset-karma can be installed via the Yarn or npm clients. Inside your project, make sure neutrino and neutrino-preset-karma are development dependencies. You will also be using another Neutrino preset for building your application source code.


❯ yarn add --dev neutrino-preset-karma


npm install --save-dev neutrino-preset-karma

Project Layout

neutrino-preset-karma follows the standard project layout specified by Neutrino. This means that by default all project test code should live in a directory named test in the root of the project. Test files end in _test.js by default.


After adding the Karma preset to your Neutrino-built project, add a new directory named test in the root of the project, with a single JS file named simple_test.js in it.

mkdir test && touch test/simple_test.js

Edit your test/simple_test.js file with the following:

import assert from 'assert';

describe('simple', () => {
  it('should be sane', () => {
    assert.equal(true, !false);

Now edit your project's package.json to add commands for testing your application. In this example, let's pretend this is a React project:

  "scripts": {
    "test": "neutrino test --use neutrino-preset-react neutrino-preset-karma"

Or if you are using .neutrinorc.js, add this preset to your use array instead of --use flags:

module.exports = {
  use: [

Run the tests, and view the results in your console:


❯ yarn test

16 02 2017 10:36:34.713:INFO [karma]: Karma v1.7.0 server started at
16 02 2017 10:36:34.715:INFO [launcher]: Launching browser Chrome with unlimited concurrency
16 02 2017 10:36:34.731:INFO [launcher]: Starting browser Chrome
16 02 2017 10:36:35.655:INFO [Chrome 56.0.2924 (Mac OS X 10.12.3)]: Connected on socket MkTbqJLpAAa2HFaeAAAA with id 21326158
    ✔ should be sane

Finished in 0.003 secs / 0 secs @ 10:36:35 GMT-0600 (CST)

✔ 1 test completed
✨  Done in 7.54s.


npm test

16 02 2017 10:38:12.865:INFO [karma]: Karma v1.7.0 server started at
16 02 2017 10:38:12.867:INFO [launcher]: Launching browser Chrome with unlimited concurrency
16 02 2017 10:38:12.879:INFO [launcher]: Starting browser Chrome
16 02 2017 10:38:13.688:INFO [Chrome 56.0.2924 (Mac OS X 10.12.3)]: Connected on socket svRGoxU0etKTKQWhAAAA with id 68456725
    ✔ should be sane

Finished in 0.006 secs / 0 secs @ 10:38:13 GMT-0600 (CST)

✔ 1 test completed

To run tests against files from your source code, simply import them:

import thingToTest from '../src/thing';

For more details on specific Karma usage, please refer to their documentation.

Executing single tests

By default this preset will execute every test file located in your test directory ending in the appropriate file extension. Use the command line files parameters to execute individual tests.

Watching for changes

neutrino-preset-karma can watch for changes on your source directory and subsequently re-run tests. Simply use the --watch flag with your neutrino test command.

Using from CI

neutrino-preset-karma needs no additional configuration to run your tests in CI infrastructure, but you will still need to ensure your CI can actually run the tests. This usually means having a display emulator and access to the browsers you are testing against.

To do this in Travis-CI, you will need to add the following to your .travis.yml file for Chrome tests:

  - export CHROME_BIN=chromium-browser
  - export DISPLAY=:99.0
  - sh -e /etc/init.d/xvfb start

Preset options

You can provide custom options and have them merged with this preset's default options, which are subsequently passed to Karma. You can modify Karma settings from .neutrinorc.js by overriding with any options Karma accepts. In a standalone Karma project this is typically done in a karma.conf.js or similar file, but neutrino-preset-karma allows configuration through .neutrinorc.js as well. This accepts the same configuration options as outlined in the Karma documentation. Use an array pair instead of a string to supply these options.

Example: Change the duration Karma waits for a browser to reconnect (in ms).

module.exports = {
  use: [
    ['neutrino-preset-karma', { browserDisconnectTimeout: 5000 }]

If you wish to completely override the Karma configuration instead of it being merged, set the override property to true in the preset options:

module.exports = {
  use: [
    ['neutrino-preset-karma', {
      override: true,
      /* specify all other Karma configuration options */


This preset is part of the neutrino-dev repository, a monorepo containing all resources for developing Neutrino and its core presets and middleware. Follow the contributing guide for details.

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